Any heat engine that performs work through internal combustion of fuel is designated as internal combustion engine. For this purpose, chemical energy from a mixture of fuel and ambient air is converted into mechanical energy by igniting said mixture in a work space of a work cylinder known as combustion chamber or combustion space. In addition to so-called continuous-flow machines or turbomachines, internal combustion engines known from the prior art, for example gasoline engines or diesel engines comprised by the equipment of conventional motor vehicles, operate according to this functional principle. For intaking ambient air and discharging combustion exhaust gases, generic motor vehicles usually are provided with intake and exhaust systems which are fluidically connected to the combustion engine, wherein said exhaust systems are also designated as exhausts in automotive engineering.
In addition to a Y-pipe, exhaust manifold and tailpipe, an exhaust for a gasoline engine known from the prior art comprises a device for reducing noise emission as it occurs in particular in the form of outlet noises of the tailpipe. For this purpose, such devices, which are known as mufflers in vehicles acoustics, can be arranged downstream of, e.g., an optionally required catalytic converter of the exhaust system, which catalytic converter, for its part, effects additional sound absorption. Attaching generic mufflers is carried out by means of appropriate mounting points on the vehicle floor.
For example, DE 100 26 355 A1 discloses a sound damping air duct for an intake duct for an air intake passage of an internal combustion engine, in particular of a motor vehicle, comprising an inner pipe that has radial openings, and comprising a sound damping cladding that encloses at least partially the inner pipe radially on the outside. In order to improve the sound-absorbing effect of this air duct, there is provided an outer pipe which completely radially encloses the inner pipe and the sound-absorbing cladding.
Also, in DE 100 58 479 A1, a wide band damper for the intake air of an internal combustion engine is proposed. This wide band damper is particularly suitable for damping the intake noise caused by the compressor for intake air. The damper is formed by a duct section which is connected to a resonant volume by means of passages. The resonant volume can annularly surround the duct section. Absorption material for improving the sound absorption is provided within the resonant volume. Furthermore, it is provided that a barrier layer is arranged between the absorption material and the passages, which barrier layer can be composed of fleece or a foil. This prevents the absorption material from being blown into the intake air where the parts of the absorption material could damage the engine. In this manner, it is intended to enable the production of a wide band damper that is cost-effective and effective over a wide band.
Furthermore, known from DE 10 2004 007 109 A1 is a silencer for an air flow channel, wherein the sound-transmitting channel is provided with openings, the length of which in the flow direction and the width of which are within a predefined size range, wherein based on a predefined opening area of the slot-like openings, a ratio of the length of the openings to the width thereof is selected, which is selected in dependence on a specific frequency range of the sound emission to be dampened, wherein the openings at the rear end as viewed in the flow direction are directed inwardly and have guiding edges protruding into the flow channel.
EP 1 170 499 A1 in turn discloses another noise reduction arrangement for air ducts. A conduit for the intake system of an internal combustion engine is formed by means of an extrusion method. The surface of the conduit is provided with orifices to allow the passage of air therethrough. This prevents the formation of standing waves in the system and thus reduces the resulting noise. The orifices can be pierced during the extrusion of the conduit and can be in the form of holes or slits. The orifices can be arranged on the conduit in a regular pattern, such as in rows, hoops or helices, or in a random pattern, or in a combination of different patterns. The orifices can also be concentrated in specific areas on the pipe surface to improve the acoustic characteristics of the pipe.
In contrast, EP 1 541 856 proposes to provide specific regions of the sound transmitting air conduit in an intake pipe of an internal combustion engine, which intake pipe serves as the sound-transmitting conduit in the curved region thereof, with slit-like orifices, the length of which in flow direction and width of which are dimensioned according to a predetermined size. Based on a predetermined orifice area of the slit-like orifices, a ratio of the length of the orifices to their width is selected in dependence on a specific frequency range of the sound emission to be absorbed. Furthermore, a closable flap is provided at the intake pipe of the internal combustion engine, which flap can be placed over the slit-like orifices provided in the curved region.
Also, from FR 2 814 778 A1, a pipe is known that has at least one porous section which, for its part, is provided with a slit that serves for reducing the noise produced by the fluid flow.
Finally, WO 1997 009 527 A1 discloses an air intake duct for a so-called reflection silencer usable in motor vehicles, which air intake duct is located between the turbocharger and the internal combustion engine and which is provided internally with screens or walls, the openings of which are at least the internal diameter of the inlet and of the outlet and align therewith. The spaces between the screens form resonance chambers for the air flowing therethrough. By choosing different opening diameters and/or different screen distances, a damping of in excess of 20 dB(A) can be achieved through a broadband in the range from 1 kHz to 5 kHz.
A disadvantage of these known devices is in some cases their one-sided optimization in view of a reduction of the outlet noise of the intake system or the absorption of certain sound frequencies.